Cellular networks have traditionally been deployed in a homogenous manner. For example, a typical cellular network may comprise a plurality of macrocells that are fairly uniform in the coverage areas they support. In the case of 3rd Generation Partnership Project (3GPP) Universal Mobile Telecommunications System (UMTS) networks, each of these macrocells is connected to a Radio Network Controller (RNC). The RNC generally effectuates radio resource management, as well as some mobility management functionality, such as facilitating handover, maintaining device state, and supporting layer 2 data-plane protocols.
There are some exceptions to the uniform deployment paradigm described above, such as picocell and femtocell networks that are deployed in conjunction with an overarching macrocellular network. That is, picocells and femtocells, which may be considered small cellular base stations or access points, connect to a service provider's core network via broadband connections, allowing the macrocellular network to be extended either for capacity augmentation or for extending the coverage (e.g., indoors). These picocells and femtocells may be deployed in the same frequency channel as the macrocellular network, in which case they are referred to as co-channel deployments, or in a different frequency channel, in which case they are referred to as dedicated channel deployments.
The overlapping nature of the cells, whether in a macrocell network or in a small-cell network, facilitates handover of a mobile device from one cell to another. A soft handover occurs when a mobile device is simultaneously connected to multiple cells. When signal quality from one of the current cells connected to the UE degrades and another cell in the neighborhood of the mobile device offers a better option, a soft handover can occur to the another cell.